Magnetorheological (MR) fluids are responsive to magnetic fields and contain a field polarizable particle component and a liquid carrier component. MR fluids are useful in a variety of mechanical applications including, but not limited to, shock absorbers, controllable suspension systems, vibration dampeners, motor mounts, and electronically controllable force/torque transfer devices.
The particle component of MR fluids typically includes micron-sized magneto-responsive particles. In the presence of a magnetic field, the magneto-responsive particles become polarized and are organized into chains or particle fibrils which increase the apparent viscosity (flow resistance) of the fluid, resulting in the development of a solid mass having a yield stress that must be exceeded to induce onset of flow of the MR fluid. The particles return to an unorganized state when the magnetic field is removed, which lowers the apparent viscosity of the fluid.
It is believed that oxidation of the magneto-responsive particles may, in some instances, compromise performance of MR fluids of which they are a component. To date, various attempts have been made to prevent or retard particle oxidation.